Suspects tied to Boston bombings – Dias Kadyrbayev, left, with Boston Marathon bombing suspect Dzhokhar Tsamaev in a picture taken from the social media site VK.com. Kadyrbayev is expected to plead guilty August 21 to charges in connection with removing a backpack and computer from Tsamaev's dorm room after the April 2013 bombing, according to a defense lawyer.

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Suspects tied to Boston bombings – Bombing suspect Tamerlan Tsarnaev was killed during the shootout with police in Watertown, Massachusetts, on April 19, 2013. He is pictured here at the 2010 New England Golden Gloves.

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Suspects tied to Boston bombings – Dzhokhar Tsarnaev was captured in a Boston suburb on April 19, 2013, after a manhunt that shut down the city. In July, he pleaded not guilty to killing four people and wounding more than 200.

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Suspects tied to Boston bombings – From left, Azamat Tazhayakov and Dias Kadyrbayev went with Boston bombing suspect Dzhokhar Tsarnaev to Times Square in this photo taken from the social media site VK.com. A federal grand jury charged Tazhayakov and Kadyrbayev with obstructing justice and conspiracy to obstruct justice relating to the removal of a backpack from Tsarnaev's dorm room after the bombings. Tazhayakov was convicted of conspiracy and obstruction charges in July 2014. He faces up to 25 years in prison at his sentencing in October. He has filed an appeal.

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Suspects tied to Boston bombings – Robel Phillipos, a U.S. citizen, was also arrested on May 1, 2013. He was charged with lying to federal agents about the bombing, according to court papers.

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Suspects tied to Boston bombings – Phillipos, Tazhayakov and Kadyrbayev are accused of removing items from Tsarnaev's dorm room after the bombings on April 15, 2013. The items they took included a backpack containing fireworks that had been "opened and emptied of powder," according to the affidavit.

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Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men identified as Suspect 1 and Suspect 2 in the deadly bombings at the Boston Marathon. They were later identified as Dzhokhar Tsarnaev, 19, and his brother Tamerlan Tsarnaev, 26.

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Suspects tied to Boston bombings – Boston Police released surveillance images of Dzhokhar Tsarnaev at a convenience store on April 19, 2013.

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Suspects tied to Boston bombings – The FBI tweeted this photo on April 19, 2013, and urged Watertown residents to stay indoors as they searched for the second suspect.

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Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men it called suspects in the deadly bombings and pleaded for public help in identifying them. The men were photographed walking together near the finish line.

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Suspects tied to Boston bombings – A man identified as Suspect 2 appeared in this photograph by bystander David Green, who took the photo after completing the Boston Marathon. Green submitted the photo to the FBI, he told Piers Morgan in an interview.

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Suspects tied to Boston bombings – The man identified as Suspect 2 appears in a tighter crop of David Green's photo.

Medical professionals at the prison medical facility, which currently houses 1,044 inmates, are making regular rounds to check on Tsarnaev, Colautti said, and Tsarnaev has spoken with staff there about managing his health.

The spokesman said he could not comment on whether Tsarnaev was speaking with investigators.

He referred questions on Tsarnaev's medical condition to the FBI, saying the facility does not assign medical condition rankings like civilian hospitals.

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Tsarnaev is in an area of the facility where there's extra security, he said.

On Friday, authorities said Tsarnaev had been transferred from Boston's Beth Israel Deaconess Medical Center to the prison facility, which is about 40 miles west of the city.

Dzhokhar Tsarnaev has been charged with using a weapon of mass destruction for his alleged role in the April 15 bombings that killed three people and injured more than 260 near the marathon's finish line.

Tsarnaev was captured April 19 after a nearly 24-hour manhunt. His brother, Tamerlan, died after a gun battle with police.

Dzhokhar Tsarnaev had what appeared to be gunshot wounds to his head, neck, legs and hand when he was captured, according to the criminal complaint accusing him in the marathon blasts.

Tsarnaev has been less talkative since authorities read him his Miranda rights three days after his capture. But the information the teenager gave investigators in two sessions of questioning has produced good leads, a U.S. law enforcement official said.

FBI: Search of dump tied to suspect ends

Since the pair of blasts turned celebratory cheers into screams of horror at the Boston Marathon's finish line, investigators have kept working -- interviewing people and searching for evidence, even when it meant sifting through trash -- to find out why.

One of the most recent focuses of the probe was a landfill in New Bedford, Massachusetts, adjacent to the town where Tsarnaev attended school at the University of Massachusetts-Dartmouth.

Authorities finished combing the dump for clues that may shed light on the bloody attack on Friday, said FBI spokeswoman Laura Eimiller, who wouldn't say whether they found anything.

A law enforcement official with knowledge of the investigation had said investigators were looking for Tsarnaev's laptop computer.

Evidence photos from Boston bombings 15 photos

Evidence photos from Boston bombings15 photos

Evidence photos from Boston bombings – A police forensics team examines a boat April 22, 2013, in Watertown, Massachusetts, where Boston Marathon bombing suspect Dzhokhar Tsarnaev was discovered several days earlier and taken into custody.

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Massachusetts State Police released thermal images of Tsarnaev hiding in the boat on April 19, 2013. They were taken by an infrared device on a helicopter. The first image was taken at 7:19 p.m., less than 20 minutes after a homeowner told police there was a bloodied person in his boat.

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This image from 7:22 p.m. shows a white heat signature large enough to be a person.

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A robotic arm tears away the cover on the boat at 7:36 p.m.

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The heat signature clearly shows the suspect's feet and the rest of his body behind the boat console at 8:01 p.m., minutes before he surrendered.

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Boston Marathon bomb scene pictures, taken by investigators, show the remains of an explosive device.

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A federal law enforcement source with firsthand knowledge of the investigation told CNN that a lid to a pressure cooker -- thought to have been used in the bombings -- had been found on a roof of a building near the scene.

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One bomb was housed in a pressure cooker hidden inside a backpack, the FBI said in a joint intelligence bulletin.

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The device also had fragments that may have included nails, BBs and ball bearings, the FBI said.

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The recovered parts include part of a circuit board, which might have been used to detonate a device.

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A law enforcement official said the bombs were probably detonated by timers. But the FBI said details of the detonating system were unknown.

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Scraps of at least one pressure cooker, nails and nylon bags were sent to the FBI's national laboratory in Virginia, where technicians will try to reconstruct the devices, the agent leading the investigation said.

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The U.S. government has warned federal agencies in the past that terrorists could turn pressure cookers into bombs by packing them with explosives and shrapnel and detonating them with blasting caps.

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The pieces suggest each of the devices was 6 liters (about 1.6 gallons) in volume, a Boston law enforcement source said.

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"It has the hallmarks of both domestic and international (attacks), and you can see either side of that," former FBI Assistant Director Tom Fuentes told CNN.

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Tsarnaev led authorities to look there, the source said, and others who may have knowledge of the computer's whereabouts or may have played a role in disposing of it also provided leads that prompted the search.

Eimiller, the FBI spokeswoman, said the investigation remains open, with interviews and the search for evidence continuing.

The wiretapped communication discussed jihad, but the conversation was vague, according to two U.S. officials. It's unclear why the Russians were eavesdropping on the mother or for how long.

One of the officials declined to say whether that wiretap information could have made a difference in ultimately uncovering a future attack on the United States.

Tom Fuentes, a CNN contributor and former FBI assistant director, said the FBI would have found that information helpful when the Russians asked U.S. investigators to look into Tamerlan Tsarnaev for a possible shift toward increasing Islamic extremism in 2011.

Family in Russia

The brothers' mother, Zubeidat Tsarnaev, said Friday that she and her husband had left their home in Dagestan for another part of Russia.

Their father, Anzor Tsarnaev, had said he'd planned to travel to the United States, but that trip has been delayed indefinitely for health reasons.

The mother has said she will not return to the United States, where she is wanted on felony charges of shoplifting and destruction of property.

The family lived in Massachusetts before Zubeidat Tsarnaev jumped bail after her arrest on the charges in 2012. The parents moved to Dagestan, a semiautonomous republic in southern Russia that year.

Zubeidat Tsarnaev has denied the reality of the bombing. She believes it was fake. She said she has seen a video pushing the wild idea, and that there was no blood, that paint was used instead.

Botched hijacking thwarts plans to head to New York

Three days after the marathon attack, and hours after authorities released images of the two suspects, they spontaneously decided to go to New York's Times Square to blow up their six remaining explosives, Dzhokhar Tsarnaev told investigators.

But a botched carjacking spoiled the impromptu road trip, said Tsarnaev, whose account was outlined by New York's police commissioner.

The vehicle they subsequently hijacked, a Mercedes sport utility vehicle, ran low on fuel, and they stopped at a service station, where the vehicle's owner escaped. Shortly thereafter, police picked up the trail of the SUV and pursued it. Authorities say the men threw bombs out the vehicle's window at them. The gun battle and Tamerlan Tsarnaev's death followed.